HERITABLE CHARACTERS OF MAIZE 



XIII— ENDOSPERM DEFECTS— SWEET DEFECTIVE AND FLINT 



DEFECTIVE 



E. \V. LiNDSTROM 



Iowa State C alley c, Ames. 



IN THE course of some inbreeding 

 experiments with maize, certain 

 unusually distinct types of defec- 

 tive kernels were isolated in commercial 

 varieties of sweet and flint corn. These 

 were merely a few of the abnormal 

 types that appear in any naturally 

 cross-fertilized crop like corn whenever 

 inbreeding- is practised. These defec- 

 tive kernels are always recessive to the 

 normal kernel type in inheritance. Their 

 recessive nature enables them to persist 

 indefinitely in the heterozygous condi- 

 tion. Dominant types may possibly 

 occur, but obviousl}- such mutants are 

 unable to reproduce their kind, since 

 the defective kernels usually fail to 

 germinate, or produce such weak seed- 

 lin';s that they eventually perish. Thus 

 ar.y dominant mutants that arise fail 

 to pass the defect to succeeding gene- 

 rations. 



The most outstanding type of defec- 

 tive grain occurred in an inbred strain 

 of the Golden Bantam variety of sweet 

 corn. This* variety is noted for its 

 stability of type, not only in its re- 

 markable quality as a table variety of 

 sweet corn, but also in its morphologi- 

 cal characteristics. Its deep yellow 

 endosperm, eight-rowed condition, 

 suckering habit and its earliness are 

 all extremely well impressed on the 

 variety. 



Inheritance of the Sweet-Defective 

 Type of Endosperm 



In 191 9 there occurred a single ear 

 among several hundred self -pollinated 

 ears of a commercial varietv of Golden 



Bantam, which showed an unusually 

 sharp segregation of normal and defec- 

 tive kernels. An actual count gave 

 134 normal and 50 defective grains. 



These off-type kernels possessed a 

 small, stunted embryo and about half 

 the usual amount of endosperm. In the 

 roasting-ear stage, the defective kernels 

 were almost as plump as the normal 

 but they showed a peculiar mottling of 

 brown in the endosperm (Figure 17). 

 On drying, they shrink to about half 

 the normal size and are a brownish- 

 gray in color ( Figure 18) . Samples were 

 given to the plant pathologist for cul- 

 ture to detect any causal organism, but 

 none was found. Germination tests 

 proved that these kernels would not 

 sprout. 



The normal grains of the original 

 ear were planted in 1920. The harvest 

 showed a distinct recurrence of the 

 defective grains. Normal grains of this 

 1920 crop were planted in the following 

 year with a similar result. 



The experimental data for these two 

 years have been arranged in Table i. 



Two sorts of progenies were found 

 among all the self -pollinated ears com- 

 ing from normal grains of a segregat- 

 ing ear. If this hereditary defect is 

 caused by a simple, recessive Alendelian 

 factor, we should expect that one sort 

 would show ears with nothing but nor- 

 mal kernels, while the other sort would 

 comprise ears with seventy-five per 

 cent normal and twenty-five per cent 

 defective grains. 



This is what actually happened as 

 can readilv be seen in Table i. The 



^ Paper No. 1 from the Department of Genetics, Iowa State College, read at the 

 Boston meeting of the A. A. A. S., December 28, 1922. 



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